A possible plot could be that Robin is initially unaware of the harem that has formed around him. The members of the harem compete in a friendly way to get his attention. But then a new villain emerges who targets Robin's loved ones. The harem then has to work together, putting aside their rivalries, to defeat the villain and protect Robin. It could show how their feelings for Robin make them stronger as a group.
Maybe in the fanfiction, the harem members are all from different backgrounds within the Young Justice universe. They are brought together by their feelings for Robin. Some are heroes, some are civilians with special knowledge. Their relationships develop as they help Robin solve a mystery that threatens the entire Young Justice world. This would involve a lot of character exploration and relationship building.
One idea could be that Robin is on a solo mission in Gotham and crosses paths with Catwoman. She initially tries to mislead him, but he sees through her tricks. They end up teaming up briefly to take down a mutual enemy who is stealing valuable artifacts from both the Batcave and Catwoman's hideouts.
Another plot could involve Robin being forced to work undercover as an assassin in a criminal organization. He has to balance his loyalty to the Young Justice and his mission to take down the organization from the inside. He might face moral dilemmas as he has to pretend to be a cold - blooded killer.
One idea could be that Robin is on a solo mission and Deathstroke is hired to stop him. Robin has to use his wits and agility to outmaneuver Deathstroke's superior strength and experience. Another could be that Deathstroke, for some reason, decides to train Robin secretly, leading to a complex relationship between the two where Robin is conflicted about learning from an enemy.
A great plot could involve Robin getting injured and Cirel having to take care of him. During this time, they have deep conversations and start to understand each other on a more personal level. This could lead to a stronger bond between them in the fanfiction.
One plot idea could be that Superboy has to navigate his relationships with different characters in the harem while also dealing with his own identity issues. For example, he might struggle with how his Kryptonian heritage affects his feelings for the other characters.
One idea could be that Robin and Artemis are on a solo mission together and get trapped in a strange, magical place. As they try to find a way out, their feelings for each other intensify. Another could be a post - battle scenario where they're both injured and have to rely on each other for care, leading to some romantic moments. Or perhaps a time - travel plot where they see alternate versions of themselves in different relationships and it makes them realize their feelings for one another.
One idea could be Robin trying to prove himself to Batman in a mission within the Young Justice framework. Maybe there's a new villain in town that only they can stop together.
One idea could be a time - travel plot where Fem Robin and Wally end up in a different era in the Young Justice universe. They have to work together to find a way back while also dealing with the challenges of that time period.
One idea could be that Robin and Wonder Woman team up for a special mission in a hidden, ancient temple. They have to solve puzzles that require both Robin's detective skills and Wonder Woman's knowledge of ancient lore. Another could be a story where Robin gets injured during a battle and Wonder Woman takes it upon herself to train him in new combat techniques to make him stronger.
Maybe there's a plot where they have a misunderstanding at first. Robin thinks Wonder Girl is too reckless in battle, while Wonder Girl believes Robin is too controlling. But through a series of events, they come to understand and respect each other more, and in the end, they become a stronger team.